1. Field
The following description relates to an analog optical transmission, and more particularly, to a technology for monitoring performance of an optical communications system based on radio over fiber (RoF).
2. Description of the Related Art
As the use of mobile data through mobile devices increases, a current mobile communications system is being developed into a form of cloud base station, which includes: a digital unit (DU) that performs functions for digital signal processing and functions of a framer and a serializer; and a radio unit (RU) with functions of an antenna and an RF amplifier and a frame division function, etc. A cloud mobile fronthaul based on a radio over fiber (Rot) uses a method of transmitting an analog signal between the DU and the RU, thereby transmitting a mobile baseband signal. However, since the analog optical signal is transmitted between the DU and the RU, a signal performance is greatly affected by the following factors: nonlinear noise and a receiver's thermal noise, which occur during the interconversion between an electrical signal and an optical signal; clipping noise generated after a part of a signal is clipped; or a linear operation area of an electrical/optical element.
Korean Patent Publication No. 10-2007-0024115 discloses an optical module used in a RoF-based communications system, and more specifically, an optical module that transmits a high-frequency signal, input from the outside, without a loss to an optical element. However, the above-mentioned patent only prevents a high-frequency signal loss, but cannot solve various degradation problems described above.